docs: def get_indices(self, src, ridx, mag):
          """
          :param src: an UCERF source
          :param ridx: a set of rupture indices
          :param mag: magnitude to use to compute the integration distance
          :returns: array with the IDs of the sites close to the ruptures
          """
          centroids = src.get_centroids(ridx)
          mindistance = min_geodetic_distance(
              (centroids[:, 0], centroids[:, 1]), self.sitecol.xyz)
          idist = self.integration_distance(DEFAULT_TRT, mag)
          indices, = (mindistance <= idist).nonzero()
          return indices